In case of infection specific immune response is concerned with the recognition and ultimate disposal of the antigen/immunogen in a highly discriminatory fashion. Specific immune responses are mediated through two types of effectors mechanisms. One is mediated by antibody produced by lymphocytes (humoral response) and the other is mediated by specially sensitized lymphocytes themselves (cell mediated immunity). The humoral responses are mainly responsible for providing prophylaxis against disease (Prophylactic vaccine) while cell mediated immunity is mainly responsible for disease intervention (Therapeutic vaccine). Prophylactic vaccines are administered in anticipation of a disease. Therapeutic vaccines are administered in presence of an active disease.
The vaccine includes antigen (s) in a pharmaceutically acceptable carrier.
An antigen is a substance that stimulates an immune response.
Varieties of antigens are described in textbooks, monographs and articles. They include immunogens allergens, varieties of material including or derived from pathogens and non pathogen's like virus, bacteria, fungi, parasites, material derived from tumors or cells. The cells, organisms like virus, bacteria are also used in the intact form e.g. Polio, BCG etc. chemical composition of antigen is widely variable and include peptides of various kinds (like plain peptides, polypeptides, Lipopeptides etc.), polysaccharides, polysaccharide conjugates, lipids, glycolipids, carbohydrates, proteins, nucleic acids or antigen encoding nucleic acids.
They are categorized in varieties of ways. Some of them are described below.
Immunogen—Any substance that provokes the immune response when introduced into the body. An immunogen is always a macromolecule (protein, polysaccharide). Its ability to stimulate the immune reaction depends on its commonness to the host, molecular size, chemical composition and heterogeneity (e.g. similar to amino acids in a protein).
Allergen—An allergen is a substance that causes the allergic reaction. It can be ingested, inhaled, injected or comes into contact with skin.
Antigens can be classified in order of their origins.
Exogenous antigens-Exogenous antigens are antigens that have entered the body from the outside, for example by inhalation, ingestion, or injection.
Endogenous antigens—Endogenous antigens are antigens that have been generated within the cell, as a result of normal cell metabolism, or because of viral or intracellular bacterial infection. The fragments are then presented on the cell surface in the complex with class 1 histocompatibility molecules.
Tumor antigens-Tumor antigens are those antigens that are presented by the MHC I molecules on the surface of tumor cells. These antigens can sometimes be presented only by tumor cells and never by the normal ones. In this case, they arc called tumor-specific antigens and typically result from a tumor specific mutation. More common are antigens that are presented by tumor cells and normal cells, and they are called tumor-associated antigens. Cytotoxic T lymphocytes that recognize these antigens may be able to destroy the tumor cells before they proliferate or metastasize.
Tumor antigens can also be on the surface of the tumor in the form of, for example, a mutated receptor, in which case they will be recognized by B cells.
Pathogen Associated Antigens
Antigens are derived from pathogens like virus, bacteria, fungus, parasites e.g. rabies, hepatitis B, mump, measles, tetanus, diphtheria etc.
Antigens can be produced by recombinant technologies, extraction methods, chemical synthesis, fermentation etc. it can be in the form of a compound or an organism which is natural or genetically modified or a fraction of an organism, which is naturally occurring or genetically modified. Nucleic acids are increasingly being developed and identified as antigens as in DNA vaccines. Antigens can be administered in the form of naked antigens, or encapsulated, coated form, conjugated, mixed, coupled and/or formulated with adjuvant.
Most of the vaccines when applied alone do not produce an adequate immune stimulus, which is addressed by use of adjuvant e.g. alum in Hepatitis B vaccine to provide desired effect.                Directly increasing the number of cells involved,        Assuring efficient processing of antigen, prolonging the duration of antigen in immunized host,        Or by increasing the antibody synthesis by antibody synthesizing cells.        
Adjuvants are substances that enhance the immune response to antigens, but are not necessarily immunogenic themselves. Adjuvants may act by retaining the antigen locally near the site of administration to produce a depot effect facilitating a slow, sustained release of antigen to cells of the immune system. Adjuvants can also attract cells of the immune system to an antigen depot and stimulate such cells to elicit immune responses.
A wide range of adjuvants provokes potent immune responses to antigens. These include saponins complexed to membrane protein antigens (immune stimulating complexes), pluronic polymers with mineral oil, killed Mycobacteria in mineral oil, Freund's complete adjuvant, bacterial products, such as muramyl dipeptide (MDP) and lipopolysaccharide (LPS), as well as lipid A, and liposomes. To efficiently induce humoral immune response (HIR) and cell-mediated immunity (CMI), antigens are preferably emulsified in adjuvants.
Currently the only adjuvant widely used in humans has been alum. It contains aluminum salts (alum) and has been useful for some vaccines like hepatitis B, diphtheria, tetanus, toxoid etc., but not useful for others like rabies MMR, typhoid etc. It fails to induce cell-mediated immunity. Aluminum hydroxide and aluminum phosphate is collectively commonly referred to as alum. Reports indicate that alum failed to improve the effectiveness of whooping cough and typhoid vaccines and provided only a slight effect with adenovirus vaccines. Problems with alum include induction of granulomas at the injection site and lot-to-lot variation of alum preparations (U.S. Pat. No. 6,861,410).
Other adjuvants, such as saponin, Qui A, and the water-in-oil adjuvant, Freund's with killed tubercle bacilli (Freund's complete) or without bacilli (Freund's incomplete), have had limited use in humans due to their toxic effects; and, concerns have been raised as to undesirable effects in animals. Most adjuvant formulations have been described but most are never accepted for routine vaccines, mainly due to their toxicity and only few have been evaluated in humans
Complete Freund's adjuvant (CFA) is a powerful immunostimulatory agent that has been successfully used with many antigens on an experimental basis. CFA includes three components: a mineral oil, an emulsifying agent, and killed Mycobacterium tuberculosis. Aqueous antigen solutions are mixed with these components to create a water-in-oil emulsion. Although effective as adjuvant, CFA causes severe side effects e.g. pain, abscess formation, fever etc. CFA, therefore, is not used in preparation of commercial vaccines.
Incomplete Freund's adjuvant (IFA) is similar to CFA but does not include the bacterial component. It is an oil in water emulsion. However, evidence indicates that both the oil and emulsifier used in IFA can cause tumors in mice.
Muramyl dipeptide (MDP) has been found to be the minimal unit of the mycobacterial cell wall complex that generates the adjuvant activity observed with CFA, e.g., Ellouz et al., Biochem. Biophys. Res. Commun. (1974) 59:1317. Several synthetic analogs of MDP have been generated that exhibit a wide range of adjuvant potency and side effects (Chedid et al., Prog. Allergy (1978) 25:63). Representative analogs of MDP include threonyl derivatives of MDP (Byars et al., Vaccine (1987) 5:223), n-butyl derivatives of MDP (Chedid et al., Infect. Immun. 35:417), and a lipophilic derivative of a muramyl tripeptide (Gisler et al., in Immunomodulations of Microbial Products and Related Synthetic Compounds (1981) Y. Yamamura and S. Kotani, eds., Excerpta Medica, Amsterdam, p. 167). One lipophilic derivative of MDP is N-acetylmuramyl-L-alanyl-D-isogluatrninyl-L-alanine-2-(1′-2′dipalmitoyl-sn-glycero-3-hydroxyphosphoryloxy)-ethylamine (MTP-PE). The MTP-PE itself is able to act as an emulsifying agent to generate stable oil-in-water emulsions. MTP-PE has been used in an emulsion of squalene with TWEEN 80, termed MTP-PE-LO (low oil), to deliver the herpes simplex virus gD antigen with effective results (Sanchez-Pescador et al., J. Immunol. (1988) 141:1720-1727), albeit with poor physical stability.
Synthetic polymers are evaluated as adjuvants. These include the homo- and copolymers of lactic and glycolic acid, which have been used to produce micro-spheres that encapsulate antigens (see Eldridge et al., Mol. Immunol. 28:287-294 (1993)).
Nonionic block copolymers are another synthetic adjuvant being evaluated. Adjuvant effects are investigated for low molecular weight copolymers in oil-based emulsions and for high molecular weight copolymers in aqueous formulations (Todd et al., Vaccine 15:564-570 (1997)).
In fact, the adjuvant effect of most experimental adjuvants has been associated with the adverse effects they elicit. Adjuvants that act as immunostimulators such as muramyl dipeptide, lipopolysaccaride, lipid A, monophosphoryl lipid A, and cytokines such as IL-2 and IL-12 can also cause systemic side-effects (general toxicity, pyrogenicity), limiting their use.
The adjuvants using whole cells like insect cells (S. frugiperda) are known (e.g., U.S. Pat. No. 6,224,882). The insects or the insect cells infected with some of the insect viruses/infectious agent or any other type of infection, also it is not yet possible to identify which insect/insect cell is infected and which not hence the use of these (i.e., insect/insect cell) can result in low production and a possible threat of transmission of disease to human (WHO report January 2005).
In an article published in Vaccine (1999) 17; 2446-2452, Bacillus of Calmette-Guerin (BCG) is used as adjuvant to rabies vaccination in mice. The experimental results show no improvement in serum neutralizing antibody titers in-group of mice immunized with BCG as adjuvant compared to plain vaccine.
U.S. Pat. No. 6,355,414 describes acemannan polysaccharide as adjuvant. U.S. Pat. No. 6,306,404 describes adjuvant & vaccine compositions of mono phosphoryl lipid A, sugar and optionally an amine-based surfactant. U.S. Pat. No. 6,231,859 describes saponin combination as adjuvant. Saponin adjuvants have high systemic toxicities, like haemolysis. The U.S. Pat. No. 6,060,068 describes interleukin-2 as adjuvant to vaccines. U.S. Pat. No. 6,355,256 describes QS-21 & IL-12 as adjuvants.
U.S. Pat. Nos. 6,103,697, 6,228,373 & 6,228,374 describes peptides as adjuvants. JP 11106351, JP 9268130 & AU 780054 describe oil adjuvants. But in all these adjuvants are not demonstrated with wide variety of antigens and mammals. Also the safety of these adjuvants is still to be confirmed.
Side effects of currently used adjuvants includes: (1) sensitization to tuberculin or any other antigen used in screening tests for infections; (2) presence in food animals of materials that cannot safely be ingested by humans; (3) inflammatory, granulomatous, necrotizing, or other unacceptable reactions at injection sites most notably as occurs with Freund's complete adjuvant; (4) pyrogenicity; (5) central nervous system effects and untoward behavioral effects; (6) impairment of growth; (7) arthritis; (8) increased vascular permeability and inflammatory reactions in the eye; (9) induction of undesired autoimmune responses and (10) immune suppression for adjuvant epitopes.
It is a long standing need of the industry to provide adjuvants that are free of above-mentioned side effects. Surprisingly, it is observed that Mycobacterium w and/or its constituents fulfill the requirement of adjuvant. Unlike Freund's adjuvant it provides immune stimulation in absence of emulsion. It is also not associated with systemic side effects like fever, body ache, muscle pain etc.
Mycobacterium w is a rapidly growing Mycobacterium. Mycobacterium w is a non-pathogenic, cultivable, atypical Mycobacterium, with biochemical properties and fast growth characteristics resembling those belonging to Runyons group IV class of Mycobacteria in its metabolic and growth properties but is not identical to those strains currently listed in this group. It is therefore thought that (Mw) is an entirely new strain. The species identity of Mw has been defined by polymerase chain reaction DNA sequence determination.
The Mycobacterium w has been found useful for treatment of Leprosy, Tuberculosis (Publication No: WO03075825-2003-09-18), and also for cancer treatment (Publication No: WO03049667-2003-06-19).
There is currently a need to have better adjuvants. The better adjuvants are needed in for improving efficacy of current vaccines like rabies wherein adjuvants like alum can not be used. They are needed to improve the efficacy of adjuvant containing current vaccines e.g. Hepatitis B vaccine containing alum. Better adjuvants are also needed to improve efficacy of various candidate vaccine so that they become effective and can be effective used e.g. CEA containing vaccines. The new adjuvants are also needed to provide novel vaccines for various new indications like vaccine for hepatic viral disease.